Elon Musk, the richest person in the world, has challenged Russian President Vladimir Putin to a duel over Ukraine.

“I hereby challenge Vladimir Putin to a man-to-man fight.

The mission is Ukraine,” the Tesla founder tweeted at the beginning of the week.

And he added in Russian: "Are you accepting this fight?"

The eccentric billionaire and founder of the aerospace company SpaceX directed the tweet to the 69-year-old Russian leader's official English-language Twitter account.

He's "absolutely serious," Musk continued, after one of his 77 million followers asked if Musk had really considered the challenge.

“If Putin could humiliate the West so easily, he would accept the challenge.

But he won't," he added.

There was no immediate reaction from the Kremlin.

Instead, Putin's ally and ruler in Chechnya, Ramzan Kadyrov, got involved.

On the Internet service Telegram he wrote to Musk: "I would not advise you to measure your strength with Putin." Because: "Your weight classes are too different."

Musk, 50, has already shown some support for Ukraine: He responded to a request from Kyiv by activating his Starlink internet service in Ukraine and sending devices to provide internet access to areas affected by Russian military attacks.